The present invention relates to a drill for the drilling of preferably metallic work pieces and a cutting insert for use in this drill.
A known drill comprises a drill shank having at least two generally axial chip flutes formed therein and at least two cutting insert sites to receive identical cutting inserts. The active cutting edge of one cutting insert projects sidewardly such that the diameter of the bore is determined thereby during a flow of chips through one chip flute. The active cutting edge of the other cutting insert is arranged radially inside the outer periphery of the drill shank and cuts chips which flow through the other chip flute.
German Patent 2730418 discloses a drill equipped with two 6-cornered inserts of mutually identical shaping received in two cutting insert sites. Each corner is formed by two edges that are mutually angled such that the bisector of each pair of edges extends parallel with the central axis of the drill.
Another type of drill is disclosed in U.S. Pat. No. 4,648,760. The inserts of this drill have a mainly rectangular shaping where each end surface of the drill is confined by two cutting edges that intersect at an obtuse angle and wherein the radially outer insert of the drill is inclined such that the size of the hole to be drilled is defined thereby, whereas the longitudinal axis of the radially inner insert extends parallel with the central axis of the drill while overlapping the same.
With drills of the aforesaid type it is difficult to achieve holes with small diameters. Further, it is difficult to use such drills for stack drilling, i.e., drilling of a plurality of plates at the same time. During such type of stack drilling there is usually formed a breakout slug. The slug will rotate with the drill and at large feed force there is a risk for cutting edge and/or drill breakdown.
The object of the present invention is to solve the above-mentioned problems.